This application claims the priority of German application 196 25 551.1-14 filed in Germany on Jun. 26, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a straight-line mechanism for slidable carriages in machine tools, having at least one straight, essentially cylindrical guiding member on which the carriage is guided.
Machine tools in the sense of the invention are those which have a slidable carriage which carries either at least one tool for machining at least one workpiece or at least one workpiece which is to be machined by at least one tool and permits a linear relative movement between the tool and the workpiece. Machine tools of this type are, for example, drilling aggregates, milling machines, grinding machines, broaching machines, injection molding machines, and the like.
As a rule, very high demands are made on the linearity of the relative movement between the tool and the workpiece and on its centricity with respect to a reference line. The acceptable machining tolerances can be maintained only if manufacturing tolerances of the machine tool as well as the wear of the guiding surfaces of the carriage can be compensated into the .mu.-range.
Accordingly, it is an object of the invention to reduce or completely eliminate also a very slight play between the guiding member and the carriage, in which case partially the displaceability of the carriage on the guiding member is maintained, but partially also eliminated and should be permitted only by means of special measures.
For achieving this object, the invention uses the idea of an earlier invention which is described and illustrated in detail in German Patent 41 09 530 and to which reference is made in this regard. In this patent, a shaft/hub connection is disclosed by which a firm connection is achieved by means of mutually coordinated profiles in a shaft and in a hub in the form of cylindrical wedges by rotating the two parts with respect to one another. These profiles each consist of at least one wedge-shaped cam which radially rises over an imaginary cylinder surface on an interior part and correspondingly of at least one wedge-shaped cam which radially rises toward the inside over an imaginary cylinder surface of a slightly larger diameter in an exterior part, which cams drop down again steeply onto the cylinder surfaces. In each arrangement the fixed connection is achieved in that the two parts are rotated so far with respect to one another that a permanent self-locking frictional engagement occurs between the parts to be connected. The frictional engagement can be eliminated without disturbance by rotating the parts back and can also be established again.
In contrast, the present invention first provides that the two parts equipped with the cylindrical wedge profiles be rotated only to such an extent that initial necessary joining play is eliminated, but the parts can still slide on one another and mainly a future wear can be compensated. By means of the invention, an intended play between the parts sliding on one another can therefore not only be initially set in a simple and precise manner but can also be adjusted later.
For this purpose, preferred embodiments of the invention provide for an arrangement of the above-noted general type, wherein the profile of the guiding member has at least three wedges which radially rise over an imaginary cylinder surface on the guiding member, are each offset by equal angles from one another in the circumferential direction and extend in a longitudinal direction of the guiding member, and wherein the profile assigned to the carriage has correspondingly arranged wedges which radially rise toward the inside over an imaginary cylinder surface of a slightly larger diameter in the carriage, and wherein the angular position of the parts having the profiles can be changed with respect to one another.
As a result, it is achieved that by rotating the parts containing the cylindrical wedge profiles, the mutual distance of the wedge surfaces and a resulting play caused by the joining play or by wear between these parts is increasingly reduced and finally eliminated or insufficient surface pressure between the parts is maintained at the intended level.
The necessary mutual rotating of the parts provided with the cylindrical wedge profiles can take place by rotating the guiding member about its longitudinal axis. However, since, as a rule, this guiding member also contributes to the stiffness of the machine tool, it is preferably provided to arrange the cylindrical wedge profiles assigned to the carriage in a bush which can be rotated in the carriage.
From German Patent Document DE 41 09 530, it is known to arrange one of the interacting profiles in a collar which can be exchanged when wear has occurred. However, this collar cannot be rotated and can therefore not be used for compensating play.
The invention can be carried out with only one cylindrical wedge pair which extends along almost the whole circumference of the guiding surface. However, preferably it is provided to equip the profiles with a plurality of wedge pairs which are arranged at equal distances, particularly with three pairs of wedges, each offset by 120.degree..
The slope of the cylindrical wedges can amount to between 1:50 and 1:200. A slope of 1:100 was found to be advantageous in many applications.
The invention can be implemented by means of only one guiding member, which is provided with the wedge profile, for a carriage. In order to prevent an uncontrolled rotating of the carriage around the guiding member, another guiding member must then be provided which, however, needs to operate only as a protection against torsion and needs to have no influence on the exact guiding of the carriage. However, as a rule, at least two guiding members are provided, for example, in the form of column guides which are then both equipped with the profiles according to the invention.
A moving of the carriage which is easy despite a most narrow adjustment can be achieved if the cylinder wedge profiles assigned to the carriage are arranged on the circumference of rotatably disposed rollers. Here also, preferably three rollers are provided which are offset by 120.degree. with respect to one another. These rollers are then also disposed in a bush which can be rotated about the longitudinal axis of the guiding member and can be fixed.
The rotating of the bush can take place manually, in which case the bush can be clamped onto the carriage by means of clamping screws which reach through concentric oblong holes.
In another embodiment, the bush can be rotationally loaded by a spring such that it is automatically rotated and adjusted when a play occurs. The force of the spring can be adjustable such that at least approximately a certain surface pressure is maintained between the wedge surfaces which slide on one another.
This automatic adjusting of the bush can have the purpose of automatically compensating occurred wear. Since at least the surface pressure and possibly even the play between the wedge surfaces depends also on the temperature of the parts sliding on one another which increases with the operating time, the automatic adjusting device can be used also for compensating these temperature-dependent operating conditions. In this case, the bush, which is cold and therefore narrow when the machine is started, can be rotated back and can then be rotated forward by the force of the spring until the endeavored surface pressure occurs in the case of the respective condition of the bush. As the operating temperature increases at which the bush rotates, the surface pressure is reduced which, however, is continuously compensated by the additional rotating of the bush under the force of the spring.
Since the rotating angles of the bush for the compensation of the changeable surface pressure, of the changeable play or of the wear are low, an endeavored surface pressure is kept uniform within narrow limits.
In another embodiment, the bearing surfaces between the bush and the carriage have profiles in the form of cylindrical wedges by means of which, as illustrated in the initially mentioned invention, they can be rotated as well as clamped in the carriage in the form of a shaft/hub connection which is fixed in this case. The two profile pairings may have the same slope. So that, during an adjusting of the bush for compensating any play between the bush and the guiding column, the frictional engagement between the bush and the carriage will not rise excessively, it is preferably provided that the profile pairing between the bush and the carriage has a lower slope of, for example, 1:200 than the profile pairing between the bush and the guiding member of, for example, 1:100.
As mentioned, the present invention first provides that the two parts equipped with the cylinder wedges be rotated only so far that the displaceability of the carriage on the guiding member is maintained. However, in some cases, it is desirable that the carriage can be locked. As a result, a so-called "rattling" of the tools, which can considerably shorten their useful life, can be avoided. Such a locking of the carriage on the guiding member can easily be achieved by means of the present invention in that the bush is rotated so far that the play between the bush and the carriage is not only largely reduced but completely eliminated and a clamping is therefore achieved. If a displacement of the carriage is to take place nevertheless, this clamping must temporarily be eliminated again.
A first possibility according to the invention exists for this purpose in that pressure oil can be introduced into the bearing surface of a bush with respect to the guiding member at such a high pressure that the bush "floats" on the guiding member and the carriage is again displaceable. When the oil pressure is reduced, the locking is reestablished.
Another possibility for temporarily eliminating the clamping consists of rotating the bush by means of an adjusting element, for example, in the form of a hydraulic cylinder so far (back) and thus to increase the play between the bush and the guiding member to such an extent that no more clamping will exist.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.